Books about snipers and marksmen!
A sniper is a marksman who shoots targets from concealed positions or distances exceeding the capabilities of regular personnel. Snipers typically have specialized training and distinct high-precision rifles.
In addition to marksmanship, military snipers are trained in camouflage, field craft, infiltration, reconnaissance and observation. Snipers are especially effective when deployed within the terrain of urban warfare, or jungle warfare.